Perhaps you should try some spelling variations:
hieu cua » hieu qua, dieu cua, bieu cua
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
tu sach » thu sach, su sach, te sach
ly nang » ky nang, ly hang, ly vang
cac luc » cau luc, coc luc, cac cuoc
ca viet » va viet, co viet, hoa viet
y nang » ky nang, v nang, may nang
va dan » ca dan, va dao, va dau
dan va » doan va, dan ca, ban va
va ca » va cac, va cao, va cai

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ((y nang) OR (ly nang)) xa hoi. hieu cua ((cac luc) or (cac nuoc)) va dan va ca viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((y nang) OR (ly nang)) xa hoi. hieu cua ((cac luc) OR (cac nuoc)) va dan va ca viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((y nang) OR (ly nang)) xa hoi. hieu cua ((cac luc) or (cac nuoc)) va dan va ca viet".
• Adding a wildcard symbol may retrieve word variants: tu sach ((y nang) OR (ly nang)) xa hoi. hieu cua ((cac luc) or (cac nuoc)) va dan va ca viet*.